1. Field of the Invention
The present invention relates to an optical disk apparatus, and more particularly to an apparatus which performs data recording/reproducing with respect to an optical disk having a pre-pit.
2. Description of Related Art
Optical disk apparatuses such as DVD-R drives and DVD-RW drives demodulate address information which is previously formed on an optical disk for determining the address, and perform data recording/reproducing. The address information is formed in such a manner that the address information is embedded by wobbling the tracks, and also in such a manner that pre-pits are formed in lands adjacent to grooves which are information recording tracks. Here, in DVD-RAMs in which both lands and grooves are information recording tracks, the address information is embedded in an embossed portion of an area formed by the embossed portion and a data portion. The present application will be described in consideration of a land pre-pit (LPP) which is formed in lands.
The land pre-pits LLPs will be described first.
One ECC block is composed of sixteen sectors 0 to 15, and each sector is composed of a total of twenty-six frames 0 to 25. These twenty-six frames can include even frames and odd frames. Generally, an LPP is disposed at the top of an even frame. However, the LPP may be disposed in the odd frames, not in the even frames, depending on the state of the adjacent track. Each LPP is composed of 3-bit data and is formed at the top of each of the thirteen frames. Consequently, in one sector, the LPPs are formed by thirteen pieces of information each having 3-bit data. For example, LPP data “111” is recorded in the 0th frame in the 0th sector, and LPP data “10X” is recorded in the 10th frame. Here, “100” represents a data value 0, and “101” represents a data value 1. The 0th to the eighth frames are areas for defining the address, while the remaining frames are used as user data, which is defined at the factory shipment of an optical disk.
A wobble signal, on the other hand, is formed by wobbling the grooves which are information recording tracks at a predetermined frequency (140 kHz), and each bit of the LPP is formed in synchronization with the peak of a wobble signal. The LPP is thus formed in synchronization with a wobble signal, and when detecting LPP from an optical disk, light reflected from the optical disk is received by a light receiving element of an optical pickup, and a reproduction signal (obtained by superimposing a wobble signal and an LPP signal) is binarized using a threshold value. As the LPP signal is superimposed on the wobble signal whose amplitude changes, the LPP signal level also changes in accordance with the change in the amplitude of the wobble signal. It is therefore difficult to extract an LPP signal correctly when a fixed threshold value is used for binarization. In order to deal with this problem, Japanese Patent Laid-Open Publications Nos. 2002-279642, 2003-59184, and 2003-91819 disclose, for example, technology in which a gate is opened only during a predetermined period in which a wobble signal has a maximum amplitude and an LPP signal is caused to pass through only when the gate is opened.
When data is recorded, synchronization information having a length of 14T (T indicates a reference signal length) is recorded at the top of each frame. According to the specification of DVD-R or the like, it is possible to select, as the 14T synchronization information, either a mark (i.e. a pit is formed by irradiation of laser light of recording power) or a space (i.e. only laser light of reproducing power is irradiated and a pit is not formed). When the mark is selected as the synchronization information, however, problems arise that such a mark affects LPP at the time of recording the mark and that LPP is affected by the mark when reproducing the LPP.
More specifically, LPP is formed in synchronization with the peak of a wobble signal as described above, and an LPP signal is superimposed on the peak of a wobble signal. It is possible to extract an LPP signal by means of an appropriate binary threshold value or window setting as long as the LPP signal has a sufficient level. When a laser power which is modulated is irradiated onto an optical disk so as to record synchronization information using a mark having a length of 14T at the position of the LPP, however, in the process of forming a mark having a length 14T by irradiation of the laser power, heat is diffused to the adjacent land, which may cause deformation of the LPP in the adjacent land, thereby lowering the LPP signal level. Further, when reproducing the synchronization information which has been recorded with a mark having a length of 14T, with the LLP signal being superimposed with a wobble signal, the LPP signal may be deformed under influence of recording of a mark having a length of 14T, thereby lowering the LPP signal level. In addition, as a mark portion having a length of 14T forms a pit, the reflectively of this portion itself is also decreased, which further makes it difficult to extract an LPP signal from a reproduction signal.
Similar problems arise when reproducing data which has been recorded. Specifically, as the synchronization information having a length of 14T and LPP exist at the synchronized position, an LPP signal is included in the 14T portion of a reproduced signal, which may cause an error in detecting the synchronization information of 14T.
Japanese Patent Laid-Open Publication No. 2003-91819 listed above discloses technology for controlling such that marks and spaces are arranged alternately as the synchronization information so as to perform ROPC (Running Optimum Power Control) reliably. With this technology, while it is possible to prevent effects of the marks on the LPP by controlling such that the synchronization information of the even frames are always set to spaces when the LPP is formed at the top of even frames, this cannot provide a satisfactory solution because the LPP may be disposed in the odd frames.